Monday, September 28, 2009

Does this donut make me look fat? Body fat percentages:

Why know your body fat percentage? Because Weight and BMI can be misleading for the active person. Neither body weight nor BMI differentiate between your fat free mass and your body fat. Your fat free mass includes bone, muscles, and organs (ACE 2003,p 183).

What are the average percents for men and women? We’ll start with the some norms. The 2003 Ace Personal Trainer Manual sites the following Body-Fat percentage categories:

Essential Fat – 2 to 5%
Athletes – 6 to 13%
Fitness – 14 to 17%
Average – 18 to 24%
Obese – 25% +

Essential fat – 10 to 13%
Athletes – 14 to 20%
Fitness – 21 to 24%
Average – 25 to 31%
Obese – 32% +

There are several ways to measure body fat, but the 2 I will disscuss here are the 2 I have experience with. Those 2 are Skinfold Measurements and Bioelectrical Impedance, they are 2 cost effective, ways to measure body fat.

Skinfold measurements are based on the belief that the amount of fat under the skin(subcutaneous fat) is proportional to the total amount of body fat (ACSM, 2009, p. 66). The standard error for this method is + 3.5% versus + 2.7% for Hydrodensitometry Weighing(the gold standard for body density measurements)(ACSM, 2009, p.66).

To measure skin folds the tester grasp subcutaneous fat and places the caliper at the 3 to 7 sites and takes an average of 3 measurements per site. The sum of the sites is calculated and referenced on a table or entered into a formula to determine body fat percentage.

Tips:The ACE 2003 Manual sites that skin fold measurements should not be taken after exercise as transfer of fluid to the skin could result in over estimation of body fat, other opportunities in error are from incorrect site determination and improperly calibrated instruments (ACE, 2003, p.187 ).

Bioelectrical Impedance is based on the principle that “the conductivity of an electrical impulse is greater through lean tissue than through fatty tissue” (ACE, 2003, p.184 ).
According to the OMRON Fat Loss Monitor manual this principle holds true because fat free mass has a higher water content and therefore conducts electricity easily, while fat has lower water content, and a lower electric conductivity. There was no listing of the accuracy of this product compared to skin fold, but it is one of the few ways to self test body fat, I am sure reliability is based on the product as most are either hand held or foot sensors. The most accurate would have sensor on the hands and feet.

How it Works:The monitor sends a low-level electric current through the body and measures the body’s resistance to electrical flow and computes body density and body fat percentage (ACE 2003, p. 184 ). Because the results of this test rely heavily on hydration you should not conduct this test: after drinking a large amount of water, after drinking alcohol, after vigorous exercise, after a bath or sauna (P7 OMRON).

Tips: OMRON manual recommends taking the measurements when the body is in homeostasis, either after waking up, 2 hours after breakfast before lunch, 2 hours after lunch before bathing or eating dinner, or 2 hours after dinner or bath and before bed. The OMRON manual also sites higher levels of error for : Body builders, athletes, people with swelling, people with fever, and children in growth stages.

So for my client participating in the Body Fat loss competition, and for the rest of you curious about where you are on the health continuum, I hope this helps to clear things up.

My reccomendation is a skin fold test by a qualified professional. Just remember, to stick with the same tool throughout your fitness program. SO if you use a body fat scale or handheld device use the same device and the same settings everytime. Also take the measurements on the same time on the same day. Your results are only as accurate as your tool.

For more reliable info on body fat percentage try these sources:

American Council on Education (2003). ACE Personal Trainer Manual: The Ultimate
Resource for Fitness professionals, Third Edition.
San Diego, CA: American Council on Exercise.

American College of Sports Medicine (2009). ACSM's Guidelines for Exercise Testing and Prescription, Eighth Edition. Philladelphia, PA: Lippincott Williams and Wilkins Publishers.

other resources used for this article:
The OMRON Body Fat Loss Manual (2008). Kyoto, Japanan: OMRON Healthcare Group.
Photos courtesy of

Health and Happiness


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